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TABLE OF CONTENTS
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PROJECT N ARRATIVE 1
CONDITIONS AND REQUIREMENTS SUMMARY
OFF-SITE ANALYSIS
FLOW CONTROL AND WATER QUALITY ANALYSIS AND DESIGN
CONVEYANCE SYSTEM ANALYSIS AND DESIGN
SPECIAL REPORTS AND STUDIES
OTHER PERMITS
ESC ANALYSIS AND DESIGN
BOND QUANTITIES, SUMMARIES, AND DECLARATION OF COVENANT
OPERATION AND MAINTENANCE MANUAL
2
5
5
8
8
8
8
8
8
TABLE OF APPENDICES
APPENDIX
SOIL INFORMATION A
SITE PLAN B
TESC PLAN C
OPERATION AND MAINTENANCE MANUAL D
DOWNSTREAM ANALYSIS E
WWHM F
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SINGH 6 TH ST SHORT PLAT TECHNICAL INFORMATION REPORT
1.0 - PROJECT OVERVIEW
This report accompanies the drainage review plan prepared for the Singh 6 th Street
Short Plat project on parcel 1023059170 in Renton, Washington. The project has been
designed to meet the requirements of the 2017 Surface Water Design Manual
(SWDM).
FIGURE 1 Vicinity Map
The existing 0.46-acre site is a developed single-family residential lot. The neighboring
parcels are also developed single-family residential lots. The parcel is a corner lot which
has frontage on Northeast 6 th Street along the south property line and frontage on Nile
Avenue Northeast along the east property line.
The project will consist of dividing the lot into two single-family residential lots, the
construction of a new single-family residence and driveway providing access to
Northeast 6 th Street and frontage improvements along Nile Avenue Northeast.
Stormwater runoff from the new residence will be dispersed on-site. The stormwater
Project Site
2
infrastructure. Predeveloped land cover characteristics are provided below in Table 1.
TABLE 1. PREDEVELOPED AREAS
Description
Area
(ft2)
Total
(ft2)
Impervious Driveway 1,681 2,117 Roof 436
Pervious Forest 13,673 13,673
Total 15,790
The soils present on the project site are identified in the NRCS soil survey as,
Alderwood gravelly sandy loam (AgC) with shallow groundwater at about 18 to 37
inches below ground.
TABLE 2. D EVELOPED AREAS
Description
Area
(ft2)
Total
(ft2)
Impervious
New ADU roof area (Lot 1) 995 1,391 New driveway (Lot 1) 396
New Residence roof a rea (Lot 2) 3,737 4,418 New driveway (Lot 2) 681
Frontage Improvements (off-site by-pass) 866 866
Pervious Landscaping 9,115 9,115
Total 15,790
2.0 CONDITIONS AND REQUIREMENTS SUMMARY
Under pre-developed conditions this property contains an existing residence, driveway,
landscaping, and detached garage which will remain on proposed Lot 1. The new Lot 2
is predominantly grassed. Along the south property line is a retaining wall to maintain
-of-way improvements.
The general slope of the land is towards the west based on topographic information per
On-site soils are identified in the NRCS Soil Survey as primarily
Alderwood gravelly, sandy loam (type C soil). A copy of the NRCS soil survey map is
provided in Appendix A.
The project will result in 6,094 square feet of total impervious surface added since
January 8th, 2001 and has more than 7,000 square feet of disturbed area. Because this
project does not qualify for Simplified Drainage Review and is not subject to Large
Project Drainage Review (more than 50 acres of project area), Directed Drainage Review
3
will be required for this project. This report will show how the project complies with
Core Requirements 1 through 9 and Special Requirements 1 through 5, as follows:
Core Requirement #1: Discharge at Natural Location
Under existing conditions, the majority of the stormwater runoff from the project site is
naturally dispersed toward the south edge of the property. This project proposes to
disperse part of the runoff from the existing and new roofs using infiltration trenches,
splashblocks and dispersion trenches. The runoff from the new driveway on Lot 1 will
disperse to the northwest with a sheet flow basic dispersion system. The remaining
impervious area will sheet flow to the south.
Core Requirement #2: Off-site Analysis
The off-site system analysis is included in Section 3.0 of this report.
Core Requirement #3: Flow Control
A WWHM analysis of the historic and developed surfaces has been completed and
included with this report. This analysis shows that the 15-minute, 100-year peak flow
rate under historic conditions from the area that will be disturbed by this project will
not be surpassed by the 15-minute, 100-year peak flow rate under developed conditions
by more than 0.15 cfs. This project is, therefore, exempt from providing flow control
facilities.
Core Requirement #4: Conveyance System
The conveyance system for this project consists of 6-inch diameter PVC pipes that
convey the stormwater to dispersion trenches. They are sized appropriately to handle
the stormwater that is anticipated.
Core Requirement #5: Erosion and Sediment Control
Erosion and sediment control requirements will be met for this project as described in
Section 4.0.
Core Requirement #6: Maintenance and Operations
The on-site stormwater features will be maintained privately by the property owner.
Operations and Maintenance provisions are addressed in Appendix D.
4
Core Requirement #7: Financial Guarantees and Liability
Financial guarantees are not anticipated to be required for this single-family project.
Core Requirement #8: Water Quality
The project is exempt from the requirement to provide basic water quality treatment
since less than 5,000 square feet of new or replaced pollution-generating impervious
surface (PGIS) is proposed that will not be fully dispersed.
Core Requirement #9: Flow Control BMPs
This project will be constructed on a lot that is less than 22,000 square feet, therefore, be
subject to Small Lot BMP Requirements, as discussed in Section 1.2.9.2.3 of the SWDM.
This project will implement the BMPs found in the list in Section 1.2.9.2.3.
Special Requirement #1: Other Adopted Area-Specific Requirements
There are no known area-specific special requirements that apply to this project site.
Special Requirement #2: Floodplain/Floodway Analysis
There are no known flood hazard areas on or adjacent to this project.
Special Requirement #3: Flood Protection Facilities
Flood protection facility special requirements do not apply to this project. The project
does not propose to construct a new or modify an existing flood protection facility.
Special Requirement #4: Source Controls
Since the proposed project is a single-family residence, source control measures are not
anticipated to be required in conjunction with this project. There is no significant
proposed outside-use or storage of pollutants.
Special Requirement #5: Oil Control
The proposed project does not require oil control measures. The site is not considered
high-use since it is a single-family residential project.
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3.0OFF-SITE ANALYSIS
Downstream Basin:
A Level 1 downstream analysis was completed for this project in July 2020.
A Level 1 downstream analysis was completed using information from King County
GIS information. The highest point of the developed site is at an elevation of about 500
feet at the northeast corner of the property. The site gently slopes from there to the
southwest. Some of the runoff continues to flow in a southwesterly direction to the
public stormwater ditch located to the south of the property and some of the runoff
passes through the neighboring lot (Parcel No. 7708200060) to the west of the property.
The runoff from the property converges at and enters the public storm drain system in
NE 6 th Street at the corner of the intersection of NE 6 th Street and 147 th Avenue SE. The
runoff then flows west through the public storm system to a public detention pond
southwest of the property. The pond discharges north to Honey Creek and continues to
flow north in the creek until it reaches a point 0.25 mile from the project site. An off-site
analysis map is included in Appendix E.
From a review of the information available relating to the downstream system. There
were no recent existing drainage problems included in the Cit
and no significant problems are anticipated as a result of the improvements proposed as
part of this project.
Upstream Tributary Basin:
There are no known concentrated sources of stormwater discharge to this property.
4.0 FLOW CONTROL AND WATER Q UALITY FACILITY ANALYSIS AND DESIGN
Flow Control
A WWHM analysis of the historic and developed surfaces has been completed and
included with this report. This analysis shows that the 15-minute, 100-year peak flow
rate under historic conditions (forest on type C soils) from the area that will be
disturbed by this project will not be surpassed by the 100-year peak flow rate under
developed conditions by more than 0.15 cfs. This project is, therefore, exempt from
providing flow control facilities. Analysis credits from Table 1.2.9.A of the SWDM were
applied to the analysis.
Under developed conditions, the portion of the property that will be disturbed for
construction will be covered by 995 square feet (0.023 acres) of ADU roof and 396
square feet (0.009 acres) of addition driveway on Lot 1. On Lot 2, the portion of the
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property that will be disturbed for construction will be covered by 3,737 square feet
(0.086 acres) of new roof and 681 square feet (0.016 acres) of new driveway.
The runoff from 1,000 square feet (0.023 acres) of the new roof will be mitigated by the
30-foot-long full infiltration trenches, 700 square feet (0.016 acres) of the new roof will
be mitigated by the splashblocks, and 700 square feet (0.016 acres) of roof area will be
mitigated by 10-foot long basic dispersion trenches on Lot 2. The runoff from 700 square
feet (0.016 acres) of roof area will be mitigated by splashblocks, and the new driveway
will be mitigated with basic dispersion by sheet flow with a 2-foot-wide gravel trench
along the northwest side of the driveway in Lot 1.
The impervious area mitigated by full infiltration, basic dispersion trenches, sheet flow,
and the splashblocks will be modeled as 10% grass and 90% impervious in the WWHM
model as allowed in Table 1.2.9.A of the SWDM.
Total
Modeled as
Impervious Lawn Pasture Removed
Roof 0.10 8 acres 0.0 56 acres 0.00 8 acres 0.000 acres 0.044 acres
New Driveway 0.037 acres 0.036 acres 0.001 acres 0.000 acres 0.000 acres
Sidewalk 0.008 acres 0.008 acres 0.000 acres 0.000 acres 0.000 acres
Landscaping 0.209 acres 0.000 acres 0.209 acres 0.000 acres 0.000 acres
Totals 0.362 acres 0.120 acres 0.218 acres 0.000 acres 0.044 acres
The WWHM model for developed conditions produced a 15-minute, 100-year peak
flow of 0.201 cfs. This is less than a 0.15 cfs increase over the predeveloped 15-minute,
100-year peak of 0.093 cfs. This project is, therefore, exempt from providing additional
flow control facilities. Detailed WWHM results are included in Appendix F.
BMPs
Section C.1.3.1 of the SWDM applies to projects on lots smaller than 22,000 square feet.
Section C.1.3.1 state that, if the proposed project is on a site/lot smaller than 22,000
square feet, then flow control BMPs must be applied as specified in Appendix C,
Section C.1.3.1 or the project must comply with the LID performance standard. This
project proposes to apply small lot BMPs to the greatest extent feasible.
Mitigation of new/replaced impervious surface:
This project is required to apply BMPs from the Small Lot BMP Requirements in Section
C.1.3.1 of Appendix C of the SWDM. The feasibility of each of those BMPs, in the order
of preference required by the manual, is discussed below.
Full Dispersion: It is infeasible to implement full dispersion BMP as detailed in
Appendix C, Section C.2.1.1 because the native vegetative flow path for full dispersion
is required to be at least 100 feet in length, which is not available on the project site.
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Full Infiltration: Full infiltration BMPs is feasible, based on information received from
Innovative Geo-Services, LLC dated April 16, 2021, the characteristics of the soils on-site
is medium sand. For each 1,000 square feet of the roof area requires 30-foot-long gravel
filled trenches as required by in Appendix C, Section C.2.2.3. There will be a 57-foot-
long gravel installed on the northwest corner of Lot 2 to mitigate total 1,900 square feet
of the roof. There is not enough space for full infiltration facilities to mitigate the
remaining new impervious area.
Limited Infiltration: For the reason discussed in the above section, there is not enough
space on site to mitigate the remaining new impervious areas. Therefore, limited
infiltration is infeasible and not required to be considered for this project.
Bioretention: For the reason discussed in the above section, there is not enough space on
site to mitigate the remaining new impervious areas. Therefore, limited infiltration is
infeasible and not required to be considered for this project.
Permeable Pavement: It is infeasible to implement permeable pavement BMP as detailed
in Appendix C, Section C.2.7.1 because the slope of the new driveway ranges from 6.5%
to 12.5% on Lot 1, and the driveway on Lot 2 has a slope more than 15%. Therefore,
permeable pavement is not feasible for this site.
Basic Dispersion: Basic dispersion, as detailed in Appendix C, Section C.2.4, will be
applied by allowing the driveway on Lot 1 to sheet flow to the west across the proposed
vegetation. There will be two splashblocks that have 50 feet of vegetated flowpath
downslope of them to mitigate the runoff from a portion of the existing roof and the
For Lot 2, there will be one splashblock that has 50 feet of vegetated
flowpath downslope of them to mitigate the runoff from the roof of the new residence.
There is not enough space to mitigate the runoff from the new 30-foot-long driveway. It
would require a minimum 25-foot setback from the property line to apply sheet flow
basic dispersion.
On Lot 1, the total new and replaced impervious area will be 1,391 square feet. On Lot 2,
4,418 square feet of new impervious areas are proposed. 2,600 square feet of the Lot 2
impervious areas will be mitigated. There will be approximately 405 square feet of
impervious areas on Lot 1 that can be traded with the new impervious areas on Lot 2
per SWDM Section 1.2.3.G.1. A total of 4,396 square feet of impervious areas will be
mitigated. The minimum required area to be mitigated by BMPs is 20% of the total lot
area. The total property area is approximately 18,812 square feet, therefore, the
minimum area to be mitigated for this project is 3,762 square feet. 4,396 square feet will
be mitigated and this satisfies the requirements of the SWDM. The remaining
impervious area is located in ROW and cannot be mitigated. The runoff that will not be
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mitigated from the site and the frontage improvements will sheet flow towards the
existing ditch along the NE 6 th Street.
Mitigation of Water Quality Impacts:
Mitigation will not be required because the project will create less than 5,000 square feet
of new pollution-generating impervious surface.
5.0 CONVEYANCE SYSTEM ANALYSIS AND DESIGN
Conveyance pipes for this project consist of a typical downspout connection that will
connect the roof runoff to the drywell in front of the proposed house. 6-inch PVC pipe
at a minimum slope of 1% will adequately convey all of the runoff from the roof to the
catch basin in front of the proposed house.
6.0 SPECIAL REPORTS AND STUDIES
A geotechnical report will be provided under a separate cover.
7.0 OTHER PERMITS
A building permit for the proposed home and ADU will be required for this project.
8.0 ESC ANALYSIS AND DESIGN
Erosion and sediment control requirements will include the delineation of clearing
limits via flagging, proper cover measures for the protection of disturbed areas,
perimeter protection with silt fencing on an as-needed basis, and a stabilized
construction entrance per City of Renton standards. The Erosion and Sediment Control
Plan has been included as part of the construction plans and is included in Appendix C.
9.0 BOND QUANTITIES, FACILITY SUMMARIES, AND DECLARATION OF
COVENANT
A bond quantities worksheet is not expected to be required by the City of Renton.
10.0 OPERATIONS AND MAINTENANCE MANUAL
The stormwater BMPs proposed for this project will be maintained privately by the
property owner. The operations and maintenance details for this private facility are
provided in the Operations and Maintenance Manual found in Appendix D
APPENDIX A:
SOIL INFORMATION
INNOVATIVE GEO-SERVICES, LLC
ENGINEERING GEOLOGY SERVICES
ENGGEOLOGIST.COM
17903 82nd ST E, Bonney Lake, WA 98391 253 279-4205 c rex@enggeologist.com
HS Construction and Investments, LLC April 29, 2021
5140 S 172nd Lane
Seatac, Washington 98188
Attn: Raman Sidhu
Singh 6th ST Short Plat Geotechnical Evaluation
Address: 615 Nile AV NE
Renton, WA
Parcel No. 1023059026
Site Visit 4/16/2021
INTRODUCTION
It is the intent of this evaluation to describe the surface and subsurface conditions on the nearly 0.44-acre
residential parcel (approx. 19,351 sf) located on the west side of Nile AV NE and north of NE 6 th ST in
Renton, WA. Development plans call for creating 1 new single family residential lot with access from NE
6th Street near the southeast corner of the new lot. The parent parcel is rectangular shaped and is
approximately 200 ft long (E/W) and approximately 100 ft. (N/S) wide.
The parent parcel will be divided into 2 residential lots which will be 0.24 to 0.20 acres in size with an
existing residential structure on the parent lot. The property has a gentle 11% grade to the southwest.
Topographically the parcel has 25 ft. of elevation change over 225 ft. The surface is covered with lawn
grasses and some berry vines.
No geologic or erosion hazards occur on the property as defined by the City of Renton, Chapter 4-3-050,
Critical Areas Regulations.
Development plans are to create 2 single-family home on the 0.44-acre property. The new homes will
utilize a municipal water and sewer, and an on-site storm water control system. The new lot will be
situated west of the existing home.
This evaluation is for the exclusive use of HS Construction and Investments, LLC, their consultants and
contractors for the intended purpose described. Site observations and exploration methods applied and
described in this evaluation are standard practices for the industry. Sources of information cited are
generally accepted resources when utilized in conjunction with field reconnaissance as confirmation.
Opinions are based on use of these standardized practices to adequately characterize the local surficial
geology and general conditions at the site.
An Engineering Geologist from Innovative GEO-Services, LLC (IGS) visited the site on April 16th, 2021 to
observe site conditions, explore near surface soil textures and conditions relating to the development of
the residential lots which will be accessed from Nile AV NE to the eastern lot and from NE 6th ST. for the
western lot. Preliminary site plans and topography were provided by AP Consulting Engineers, PLLC.
Additional information was obtained from the King County GIS system.
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SITE AND PROJECT DESCRIPTION
The residential parcel is a nearly rectangular shaped property with two distinct topographic areas. The
eastern portion of land is level to gently sloping to the west while the western lot slopes to the southwest
with gentle grades. The eastern parcel contains a single-family residential structure which is currently
being remodeled. The western lot is undeveloped.
Access to the property is from SE 270 th ST near the northeast corner of the parcel. Development plans
show the new home will be situated in the north third of the parcel where the surface is nearly level. The
proposed development is surrounded by similar residential development and access. The surrounding
homes are typically wood framed structures which utilize conventional foundation systems.
SINGH 6TH STREET PLAT SITE PLAN
EXPLORATION MAP
Site Plan Provided by AP Consulting Engineers, PLLC (nts)
IGS SOIL PITS (4/16/2021)
SP 3
SP 4
EXISTING
HOUSE
11%
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SITE SOILS
The Natural Resource Conservation Service (NRCS) describe the soils across the parcel as Alderwood
gravelly sandy loam (AgC).
NRCS SOIL MAPPING
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NRCS SOIL CLASSIFICATION
Alderwood AgC Alderwood gravelly sandy loam, 6 15 percent slopes
The Alderwood gravelly sandy loam is moderately well drained. It formed in glacial till on broad uplands.
It is extensive in the Lake Tapps area. Predominant native vegetation is made up of hardwoods and
conifers. The typical elevation of this soil series ranges from 200 to 800 feet.
In a typical soil profile, a mat of undecomposed needles and wood fragments rests upon a 1 ½ inch thick
very dark grayish brown gravelly sandy loam surface layer. The subsoil and the upper part of the
substratum, to a depth of 38 inches, are dark yellowish brown, brown, and dark grayish brown gravelly
sandy loam. The lower portion of the substratum, to a depth of more than 60 inches, is weakly cemented
compact glacial till. A seasonal water table is perched above the very slowly permeable, weakly cemented
and compact part of the substratum during periods of heavy rainfall. However, the perched water table is
of short duration because the water flows laterally above this layer to seeps at the bottom of slopes. Very
few roots penetrate this dense substratum. The available water capacity is low. Surface runoff is medium,
and the erosion hazard is moderate.
This rolling Alderwood soil is moderately well drained. It formed in glacial till on broad uplands. It is
extensive in the Lake Tapps area. Vegetation is hardwoods and conifers. Elevation ranges from 200 to 800
feet. The mean annual precipitation is about 35 inches, mean annual air temperature is about 50 degrees
F, and the frost- free season averages about 180 days. Individual soil areas average about 125 acres in
size. Most slopes average about 8 percent. Granite boulders and stones are strewn across some slopes.
Included with this soil in mapping are small areas of better drained Indianola loamy sand on the side slopes
and poorer drained Norma sandy loam or Dupont muck in troughs. In addition, some areas of Alderwood
gravelly sandy loam and Kapowsin gravelly loam, zero to six percent slopes, are included.
In a typical soil profile, a mat of undecomposed needles and wood fragments rests upon a 1 ½ inch thick
very dark grayish brown gravelly sandy loam surface layer. The subsoil and the upper part of the
substratum, to a depth of 38 inches, are dark yellowish brown, brown, and dark grayish brown gravelly
sandy loam. The lower parrot of the substratum, to a depth of more than 60 inches, is weakly cemented
compact glacial till. Reaction is medium acid.
The water table is perched above the very slowly permeable, weakly cemented and compact part of the
substratum during periods of heavy rainfall. However, the perched water table is of short duration because
the water flows laterally above this layer to seeps at the bottom of slopes. Very few roots penetrate this
dense substratum. The available water capacity is low. Surface runoff is medium, and the erosion hazard
is moderate.
Because of its proximity to urban centers, this Alderwood soil is subject to urbanization pressure. The soil
has an inherent ability to support a large load. Soil slope and the weakly cemented, compact substratum
are its limiting features. In areas of moderate to high population density, onsite sewage disposal systems
often fail or do not function properly during periods of rainfall in winter. Excavation for basements and
utility lines is difficult to cover excavated soil material.
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SITE GEOLOGY
According to maps from the Washington Division of Geology and Earth Resources, this region of King
County lies in the glacial lowland area of multiple glacial advance and recessional periods. The surface
deposits are described as Proglacial stratified drift deposits of gravelly sands, fine sands described as
ground moraine deposits.
Moraines may form through a number of processes, depending on the characteristics of sediment, the
dynamics on the ice, and the location on the glacier in which the moraine is formed. Moraine forming
processes may be loosely divided into passive and active. Passive processes involve the placing of chaotic
supraglacial sediments onto the landscape with limited reworking, typically forming hummocky moraines.
These moraines are composed of supraglacial sediments from the ice surface. Active processes form or
rework moraine sediment directly by the movement of ice, known as glacio-tectonism. These forms push
moraines and thrust-block moraines, which are often composed of till and reworked proglacial sediment.
Moraine may also form by the accumulation of sand and gravel deposits from glacial streams emanating
from the ice margin. These fan deposits may coalesce to form a long moraine bank marking the ice margin.
Several processes may combine to form and rework a single moraine, and most moraines record a
continuum of processes.
Ground moraines are till-covered areas with irregular topography and no ridges, often forming gently
rolling hills or plains. They are accumulated at the base of the ice as lodgment till, but may also be
deposited as the glacier retreats. In alpine glaciers, ground moraines are often found between the two
lateral moraines. Ground moraines may be modified into drumlins by the overriding ice.
Geologic Map of King County (Excerpt)
Compiled by Booth, Troost & Wisher, March 2007
Qvt
SINGH 6TH ST PLAT
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City of Renton Critical Area Regulations
4-3-050B APPLICABILITY:
1. Lands to Which These Regulations Apply and Non-regulated Lands:The following critical
areas are regulated by this Section. Multiple development standards may apply to a site feature
based upon overlapping critical area(s) and/or critical area classifications:
a. Flood hazard areas.
b. Steep slopes (must have a minimum vertical rise of fifteen feet (15')), landslide hazards, erosion
hazards, seismic hazards, and/or coal mine hazards or on sites within fifty feet (50') of steep
slopes, landslide hazards, erosion hazards, seismic hazards, and/or coal mine hazards classified
under RMC 4-3-050G5a which are located on abutting or adjacent sites.
c. Habitat Conservation Areas.
d. Streams and Lakes. All applicable requirements of this Section apply to Class F, Np, and Ns
water bodies, as defined in subsection G7 of this Section or on sites within one hundred feet
(100') of Class F, Np, and Ns water bodies, except Type S water bodies, inventoried as
bject to this Section, and are regulated in RMC 4-3-090,
Shoreline Master Program Regulations, and RMC 4-9-190, Shoreline Permits.
e. Wellhead Protection Areas.
f. Wetlands, Categories I, II, III, and IV or on sites within two hundred feet (200') of Category I, II,
III, and IV wetlands.
Wetlands created or restored as a part of a mitigation project are regulated wetlands. Regulated wetlands
do not include those artificial wetlands intentionally created from no wetland sites, including, but not limited
to, irrigation and drainage ditches, grass-lined swales, canals, detention facilities, wastewater treatment
facilities, farm ponds, and landscape amenities, or those wetlands created after July 1, 1990, that were
unintentionally created as a result of the construction of a road, street, or highway.
g.Sites Separated from Critical Areas, Nonregulated:As determined by the Administrator,
these regulations may not apply to development proposed on sites that are separated from critical
areas by pre-existing, intervening, and lawfully created structures, roads, or other substantial
existing improvements. For the purposes of this Section, the intervening lots/parcels, roads, or
other substantial improvements shall be found to:
i. Separate the subject upland property from the critical area due to their height or width; and
ii. Substantially prevent or impair delivery of most functions from the subject upland property to
the critical area. Such determination and evidence shall be included in the application file. Public
notification shall be given as follows:
(a) For applications that are not subject to notices of application pursuant to Chapter 4-8
RMC, notice of the buffer determination shall be given by posting the site and notifying
parties of record, if any, in accordance with Chapter 4-8 RMC.
(b) For applications that are subject to notices of application, the buffer determination or
request for determination shall be included with notice of application. Upon
determination, notification of parties of record, if any, shall be made.
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Findings
Based on our site observations, explorations and research it is our opinion there are no geologic hazards
as defined by the City of Renton occur on or near the proposed development. The proposed new
residential lots are proposed across gentle grades.
The property is underlain by a massive deposit of glacial till. This glacial till dominates the regions and
consists of a very dense, nearly impermeable compressed silty sand and gravel. The upland area and
surface deposits are consistent with weathered glacial till.
No steep slopes as defined by the City occur on or adjacent to the property . Our site observations and
research found no indications of current or past morphology consistent with landslide activity.
Site Preparation
Preparation of the project site should involve erosion control, temporary drainage, clearing, stripping,
cutting, filling, excavations, and subgrade compaction.
Erosion Control: Before new construction begins, an appropriate erosion control system should be
installed. This system should collect and filter all surface run off through either silt fencing or a series of
properly placed and secured straw bales. We anticipate a system of berms and drainage ditches around
construction areas will provide an adequate collection system. If silt fencing is selected as a filter, this
fencing fabric should meet the requirements of WSDOT Standard Specification 9-33.2 Table 3. In addition,
silt fencing should embed a minimum of 6 inches below existing grade. If straw baling is used as a filter,
bales should be secured to the ground so that they will not shift under the weight of retained water.
Regardless of the silt filter selected, an erosion control system requires occasional observation and
maintenance. Specifically, holes in the filter and areas where the filter has shifted above ground surface
should be replaced or repaired as soon as they are identified.
Temporary Drainage: We recommend intercepting and diverting any potential sources of surface or
near-surface water within the construction zones before stripping begins. Because the selection of an
appropriate drainage system will depend on the water quantity, season, weather conditions, construction
sequence, and contractor's methods, final decisions regarding drainage systems are best made in the field
at the time of construction. Based on our current understanding of the construction plans, surface, and
subsurface conditions, we anticipate that curbs, berms, or ditches placed around the work areas will
adequately intercept surface water runoff.
Clearing and Stripping: After surface and near-surface water sources have been controlled, the
construction areas should be cleared and stripped of all duff and topsoil. Also, it should be realized that
if the stripping operation proceeds during wet weather, a generally greater stripping depth might be
necessary to remove disturbed moisture-sensitive soils; therefore, stripping is best performed during a
period of dry weather.
Site Excavations: Based on our explorations, we expect site excavation will encounter dense to very
dense gravelly sand with cobbles. Special teeth on excavators or rippers on bulldozers may be needed to
rapidly excavate these soils. Excavations over 4 ft in depth may require side wall support.
Dewatering: Explorations did not observe groundwater at elevations where earth work activity will occur,
nor do we expect that groundwater will be present in excavations for the planned development. However,
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if groundwater is encountered, we anticipate that an internal system of ditches, sump holes, and pumps
will be adequate to temporarily dewater excavations.
Temporary Cut Slopes: All temporary soil slopes associated with site cutting or excavations should be
adequately inclined to prevent sloughing and collapse. Temporary cut slopes in loose gravelly sand should
be no steeper than 1½H:1V and should conform to WISHA regulations
Subgrade Compaction: Exposed subgrades for footings and floors should be compacted to a firm,
unyielding state before new concrete or fill soils are placed. Any localized zones of looser granular soils
observed within a subgrade should be compacted to a density commensurate with the surrounding soils.
In contrast, any organic, soft, or pumping soils observed within a subgrade should be over excavated and
replaced with a suitable structural fill material.
Site Filling: Our conclusions regarding the reuse of on-site soils and our comments regarding wet-weather
filling are presented subsequently. Regardless of soil type, all fills should be placed and compacted
according to our recommendations presented in the Structural Fill section of this report. Specifically,
building pad fill soil should be compacted to a uniform density of at least 95 percent (based on ASTM:D-
1557).
On-Site Soils: We offer the following evaluation of these on-site soils in relation to potential use as
structural fill:
Surficial Organic Soils: The duff and topsoil mantling some of the sites are not suitable
for use as structural fill under any circumstances, due to their high organic content.
Consequently, these materials can be used only for non-structural purposes, such as in
landscaping areas.
Weathered and Unweather Glacial Till: The weathered and weathered glacial till layers
are sensitive to moisture content variations. These soils can be reused during dry
conditions but will become increasingly difficult to reuse as conditions become wetter.
Permanent Slopes: Permanent cut slopes and fill slopes are not anticipated or shown on current designs.
If permanent cut or fill slopes are incorporated, they should be adequately inclined to minimize long-term
raveling, sloughing, and erosion. We generally recommend no permanent slopes be steeper than 2H:1V.
For all soil types, the use of flatter slopes (such as 2½H:1V) would further reduce long-term erosion and
facilitate revegetation.
Spread Footings
In our opinion, conventional spread footings will provide adequate support for the residential structures
if the subgrades are properly prepared.
Footing Depths and Widths: For frost and erosion protection, the bases of all exterior footings should
bear at least 18 inches below adjacent outside grades, whereas the bases of interior footings need bear
only 12 inches below the surrounding slab surface level. To reduce post-construction settlements,
continuous (wall) and isolated (column) footings should be at least 18 and 24 inches wide, respectively.
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Bearing Subgrades: Footings should bear on medium dense or denser, undisturbed native soils which
have been stripped of surficial organic soils, or on properly compacted structural fill which bears on
undisturbed native soils which have been stripped of surficial organic soils. In general, before footing
concrete is placed, any localized zones of loose soils exposed across the footing subgrades should be
compacted to a firm, unyielding condition, and any localized zones of soft, organic, or debris-laden soils
should be over excavated and replaced with suitable structural fill. Care should be taken in identifying
pockets of loose fill, placed during prior grading activities, which may be scattered across the site.
Subgrade Observation: All footing subgrades should consist of firm, unyielding, native soils or structural
fill materials compacted to a density of at least 95 percent (based on ASTM:D-1557). Footings should never
be cast atop loose, soft, or frozen soil, slough, debris, existing uncontrolled fill, or surfaces covered by
standing water.
Bearing Pressures: For static loading, footings which bear on properly prepared subgrades can be
designed for a maximum allowable soil bearing pressure of 2,000 pounds per square foot (psf). A one-
third increase in allowable soil bearing capacity may be used for short-term loads created by seismic or
wind related activities.
Footing Settlements: Assuming structural fill soils are compacted to a medium dense or denser state, we
estimate that total post-construction settlements of properly designed footings bearing on properly
prepared subgrades will not exceed 1 inch. Differential settlements for comparably loaded elements may
approach one-half of the actual total settlement over horizontal distances of approximately 50 feet.
Footing Backfill: To provide erosion protection and lateral load resistance, it is recommended all footing
excavations be backfilled on both sides of the footings and stem walls after the concrete has cured. Either
imported structural fill or non-organic on-site soils can be used for this purpose, contingent on suitable
moisture content at the time of placement. Regardless of soil type, all footing backfill soil should be
compacted to a density of at least 90 percent (based on ASTM:D-1557).
Lateral Resistance: Footings that have been properly backfilled as recommended above will resist lateral
movements by means of passive earth pressure and base friction. We recommend using an allowable
passive earth pressure of 300 pcf in the glacial till onsite, 250 pcf in the glacial outwash onsite, and 160
pcf for the silt onsite. We recommend an allowable base friction coefficient of 0.35 for glacial till and
outwash, and 0.20 for silt.
Slab-On-Grade Floors
Soil-supported slab-on-grade floors can be used in the proposed structures if the subgrades are properly
prepared. We offer the following comments and recommendations concerning slab-on-grade floors.
Floor Subbase: Structural fill subbases do not appear to be needed under soil-supported slab-on-grade
floors at the site. However, the final decision regarding the need for subbases should be based on actual
subgrade conditions observed at the time of construction. If a subbase is needed, all subbase fills should
be compacted to a density of at least 95 percent (based on ASTM:D-1557).
Capillary Break and Vapor Barrier: To retard the upward wicking of groundwater beneath the floor slab,
we recommend that a capillary break be placed over the subgrade. Ideally, this capillary break would
consist of a 4-inch-thick layer of pea gravel or other clean, uniform, well-
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-03.12(4), but clean angular gravel can be used if
it adequately prevents capillary wicking. In addition, a layer of plastic sheeting (such as Crosstuff,
Visqueen, or Moistop) should be placed over the capillary break to serve as a vapor barrier. During
subsequent casting of the concrete slab, the contractor should exercise care to avoid puncturing this vapor
barrier.
Drainage Systems
In our opinion, the proposed new structures should be provided with permanent drainage systems to
reduce the risk of future moisture problems. We offer the following recommendations and comments for
drainage design and construction purposes.
Perimeter Drains: Site soil characteristics observed indicate the use of footing drains is optional. Footing
drains if utilized are a perimeter drain system to collect seepage water. This drain should consist of a 4-
inch-diameter perforated pipe within an envelope of pea gravel or washed rock, extending at least 6
inches on all sides of the pipe, and the gravel envelope should be wrapped with filter fabric to reduce the
migration of fines from the surrounding soils. Ideally, the drain invert would be installed no more than 8
inches above the base of the perimeter footings.
Subfloor Drains: Based on the groundwater conditions observed in our site explorations, we do not infer
a need for subfloor drains.
Discharge Considerations: If possible, all storm water drains should discharge to an approved infiltration
system or other suitable location by gravity flow. Check valves should be installed along any drainpipes
that discharge to a sewer system, to prevent sewage backflow into the drain system.
Runoff Water: Roof-runoff and surface-runoff water should not discharge into the perimeter drain system.
Instead, these sources should discharge into separate tight line pipes and be routed away from the
building to a storm drain or other appropriate location.
Grading and Capping: Final site grades should slope downward away from the buildings so that runoff
water will flow by gravity to suitable collection points, rather than ponding near the building. Ideally, the
area surrounding the building would be capped with concrete, asphalt, or low-permeability (silty) soils to
minimize or preclude surface-water infiltration.
Infiltration Rates: Soil characteristics and grain size observed in two soil pits excavated across the parcel
found the native soil to be a fine sand and silt with some gravel (weathered Glacial Till) transitioning to a
very dense gray glacial till. Raw infiltration rates in the upper 36 to 48 inches of soil can anticipate 10
in/hr. or less in the Alderwood soil based on the observed soil and grain size. We recommend storm
water control plans use surface dispersion to the north side of the new home. Soil infiltration logs are
attached to this report.
Structural Fill
The term "structural fill" refers to any placed under foundations, retaining walls, slab-on-grade floors,
sidewalks, pavements, and other structures. Our comments, conclusions, and recommendations
concerning structural fill are presented in the following paragraphs.
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Materials: Typical structural fill materials include clean sand, gravel, pea gravel, washed rock, crushed
rock, well-graded mixtures of sand and gravel (commonly called "gravel borrow" or "pit-run"), and
miscellaneous mixtures of silt, sand, and gravel. Recycled asphalt, concrete, and glass, which are derived
from pulverizing the parent materials, are also potentially useful as structural fill in certain applications.
Soils used for structural fill should not contain any organic matter or debris, nor any individual particles
greater than about 6 inches in diameter.
Fill Placement: Clean sand, gravel, crushed rock, soil mixtures, and recycled materials should be placed in
horizontal lifts not exceeding 8 inches in loose thickness, and each lift should be thoroughly compacted
with a mechanical compactor.
Compaction Criteria: Using the Modified Proctor test (ASTM:D-1557) as a standard, we recommend that
structural fill used for various on-site applications be compacted to the following minimum densities:
Fill Application Minimum
Compaction
Footing subgrade and bearing pad
Foundation backfills
Slab-on-grade floor subgrade and subbase
95 percent
90 percent
95 percent
Subgrade Observation and Compaction Testing: Regardless of material or location, all structural fills
should be placed over firm, unyielding subgrades prepared in accordance with the Site Preparation section
of this report. The condition of all subgrades should be observed by geotechnical personnel before filling
or construction begins. Also, fill soil compaction should be verified by means of in-place density tests
performed during fill placement so that adequacy of soil compaction efforts may be evaluated as
earthwork progresses.
Soil Moisture Considerations: The suitability of soils used for structural fill depends primarily on their
grain-size distribution and moisture content when they are placed. As the "fines" content (that soil
fraction passing the U.S. No. 200 Sieve) increases, soils become more sensitive to small changes in
moisture content. Soils containing more than about 5 percent fines (by weight) cannot be consistently
compacted to a firm, unyielding condition when the moisture content is more than 2 percentage points
above or below optimum. For fill placement during wet-weather site work, we recommend using "clean"
fill, which refers to soils that have a fines content of 5 percent or less (by weight) based on the soil fraction
passing the U.S. No. 4 Sieve.
RECOMMENDED ADDITIONAL SERVICES
Because the future performance and integrity of the structural elements will depend largely on proper
site preparation, drainage, fill placement, and construction procedures, monitoring and testing by
experienced geotechnical personnel should be considered an integral part of the construction process.
Consequently, we recommend that IGS be retained to provide the following post-report services:
Review all construction plans and specifications to verify that our design criteria
presented in this report have been properly integrated into the design.
Prepare a letter summarizing all review comments (if required by the City of Renton).
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Check all completed subgrades for footings and slab-on-grade floors before concrete is
poured, to verify their bearing capacity; and
Prepare a post-construction letter summarizing all field observations, inspections, and
test results (if required).
CLOSURE
The conclusions and recommendations presented in this report are based, in part, on the explorations
that we performed for this study; therefore, if variations in the subgrade conditions are observed at a
later time, we may need to modify this report to reflect those changes. Also, because the future
performance and integrity of the project elements depend largely on proper initial site preparation,
drainage, and construction procedures, monitoring and testing by experienced geotechnical personnel
should be considered an integral part of the construction process. IGS is available to provide geotechnical
monitoring of soils throughout construction.
Innovative GEO-Services, LLC
Rex Humphrey, L.E.G.
Engineering Geologist
04/30/2021
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SOIL TEST PIT LOGS
SOIL TEST PITS 1 THROUGH 4
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Soil Log Number: 3
Sheet 1 of 1
1. Site Address: 56XX NE 6th Street, Renton
2. Parcel Number: 102305170
3. Site Description: Glacial Terrace
4. List methods used to expose, sample, & test soils:
Excavation of Test Pits and Field Examination
5. Number of test holes logged: 4
6. Saturated Percolation Rate:
10 in/hr.
7. Has fill material been placed over the proposed
infiltration area?
No
8. SCS Soil Series
Alderwood
9. Hydrologic Soil Group
C
10. Depth to seasonal high water:
4 ft.
11. Current water depth
> 4 ft.
12. Depth to impermeable layer:
>/= 4 ft.
13. Soil profile description:
1 Dk Brown, Sandy Loam w/ gravel
2 - Lt Brown Sandy loam w/ gravel
3 Glacial Till, gray, dry
Horizon Depth Textural Class Mottling Induration
1
2
3
0 4 in.
4 - 36 in.
36 48 in
IV
IV
IV
-
-
Slight
.
I hereby state that I prepared this report and conducted or supervised the performance of related work. I state
that I am qualified to do this work. I represent my work to be complete and accurate within the bounds of
uncertainty inherent to the practice of soil science, and to be suitable for its intended use.
Date: 04/29/2021
Registration No.: 1811
Stamp
4/29/2021
APPENDIX B:
SITE PLAN
APPENDIX C:
TEMPORARY EROSION AND
SEDIMENT CONTROL PLAN
APPENDIX D:
OPERATION & MAINTENANCE MANUAL
SIGNH 6TH STREETS SHORT PLAT
STORM DRAINAGE FACILITIES
OPERATION AND MAINTENANCE MANUAL
Site Address:
The development will occur on tax parcel number 1023059170. The existing residence on
Lot 1 of this project s short plat is located at 603 Nile Avenue NE in Renton, WA. The new
residence on Lot 2 of this project s short plat is located at 56XX NE 6th Street in Renton,
WA.
Introduction:
This storm drainage report has been prepared to address the City of site
development and storm drainage requirements for the proposed Singh 6th Street Short
Plat for parcel number 1023059170. The portion of the site that will be disturbed for
construction has an area of approximately 0.225 acres. The subject site will be divided
into two single-family lots and be developed by constructing of a new single-family
residence and driveway with stormwater control features and frontage improvements
for the new lots.
According to the City of standards for stormwater management, the City
requires stormwater quantity and quality control for all proposed developments where
to construct dispersion systems consisting of infiltration trenches, splash blocks,
dispersion trenches, yard drain/catch basins, and tightlines to address the required
portion of the stormwater coming from the new impervious areas.
Plan Goal:
The specific purpose for the stormwater facility is to mitigate runoff from the proposed
impervious areas. Attached to this narrative is a maintenance manual, which offers
guidelines to the owner for stormwater facility maintenance.
DRAINS TO
STREAM.
stenciling and providing spill control procedures. In case of spill call the Washington
State Department of Ecology at (425) 649-7000. The catch basins must be visually
inspected for accumulation of debris and silt and will be maintained as required by this
operation and maintenance manual and attachments.
Maintenance Standards for Drainage Facilities:
No. 2 Infiltration Facilities
No. 5 - Catch Basins
No. 27 - Dispersion Trenches
The City of Renton Utilities Section is to review and approve any changes to this
Operation and Maintenance Manual prior to changes in its implementation.
Additionally, any changes in ownership or person of responsibility are to be reported to
the City Utilities Section.
Inspection/Maintenance:
Regular inspections of the drainage facilities should be carried out twice per year, in the
spring and fall. The responsible party should keep records of these inspections available
for review by the City. Additional inspections may be required after severe seasonal
storms.
Routine maintenance of the site will include mowing, care of landscaping, and the
removal of trash and debris from the drainage system. The driveway should be kept clean
and in repair. Events such as major storms or heavy winds will require immediate
inspections for damages.
Catch basins shall be cleaned when sump contains four inches or more of sediment or
debris.
Person of Responsibility:
Harry Singh & Molly Sablok
603 Nile Ave NE
Renton, WA 98059
Design Engineer:
AP Consulting Engineers PLLC
Adam E. Paul, PE
PO Box 162
Auburn, WA 98071
INSPECTION/MAINTENANCE CHECKLIST
STRUCTURE
RESULTS/
MAINTENANCE DATE NOTES
All Catch Basins Inspection results
Maintenance Done
Control Structures Inspection Results
Maintenance Done
Dispersion Trenches Inspection Results
Maintenance Done
The facility-specific maintenance standards that follow this checklist are intended to be
conditions for determining through inspection if maintenance actions are required.
Exceeding these conditions at any time between inspections and/or maintenance actions
does not automatically constitute a violation of these standards. However, based upon
inspection observations, the inspection and maintenance schedules shall be adjusted to
minimize the length of time that a facility is in a condition that requires a maintenance
action.
APPENDIX A MAINTENANCE REQUIREMENTS FOR FLOW CONTROL, CONVEYANCE, AND WQ FACILITIES
NO. 2 – INFILTRATION FACILITIES
Maintenance
Component
Defect or Problem Conditions When Maintenance Is Needed Results Expected When
Maintenance Is Performed
Site Trash and debris Any trash and debris which exceed 1 cubic foot
per 1,000 square feet (this is about equal to the
amount of trash it would take to fill up one
standard size office garbage can). In general,
there should be no visual evidence of dumping.
Trash and debris cleared from site.
Noxious weeds Any noxious or nuisance vegetation which may
constitute a hazard to County personnel or the
public.
Noxious and nuisance vegetation
removed according to applicable
regulations. No danger of noxious
vegetation where County personnel
or the public might normally be.
Contaminants and
pollution
Any evidence of contaminants or pollution such
as oil, gasoline, concrete slurries or paint.
Materials removed and disposed of
according to applicable regulations.
Source control BMPs implemented if
appropriate. No contaminants
present other than a surface oil film.
Grass/groundcover Grass or groundcover exceeds 18 inches in
height.
Grass or groundcover mowed to a
height no greater than 6 inches.
Infiltration Pond,
Top or Side Slopes
of Dam, Berm or
Embankment
Rodent holes Any evidence of rodent holes if facility is acting
as a dam or berm, or any evidence of water
piping through dam or berm via rodent holes.
Rodents removed or destroyed and
dam or berm repaired.
Tree growth Tree growth threatens integrity of dams, berms
or slopes, does not allow maintenance access,
or interferes with maintenance activity. If trees
are not a threat to dam, berm, or embankment
integrity or not interfering with access or
maintenance, they do not need to be removed.
Trees do not hinder facility
performance or maintenance
activities.
Erosion Eroded damage over 2 inches deep where cause
of damage is still present or where there is
potential for continued erosion. Any erosion
observed on a compacted slope.
Slopes stabilized using appropriate
erosion control measures. If erosion
is occurring on compacted slope, a
licensed civil engineer should be
consulted to resolve source of
erosion.
Settlement Any part of a dam, berm or embankment that
has settled 4 inches lower than the design
elevation.
Top or side slope restored to design
dimensions. If settlement is
significant, a licensed civil engineer
should be consulted to determine
the cause of the settlement.
Infiltration Pond,
Tank, Vault, Trench,
or Small Basin
Storage Area
Sediment
accumulation
If two inches or more sediment is present or a
percolation test indicates facility is working at or
less than 90% of design.
Facility infiltrates as designed.
Liner damaged
(If Applicable)
Liner is visible or pond does not hold water as
designed.
Liner repaired or replaced.
Infiltration Tank
Structure
Plugged air vent Any blockage of the vent. Tank or vault freely vents.
Tank bent out of
shape
Any part of tank/pipe is bent out of shape more
than 10% of its design shape.
Tank repaired or replaced to design.
Gaps between
sections, damaged
joints or cracks or
tears in wall
A gap wider than ½-inch at the joint of any tank
sections or any evidence of soil particles entering
the tank at a joint or through a wall.
No water or soil entering tank
through joints or walls.
Infiltration Vault
Structure
Damage to wall,
frame, bottom, and/or
top slab
Cracks wider than ½-inch, any evidence of soil
entering the structure through cracks or qualified
inspection personnel determines that the vault is
not structurally sound.
Vault is sealed and structurally
sound.
2016 Surface Water Design Manual – Appendix A 4/24/2016
A-3
APPENDIX A MAINTENANCE REQUIREMENTS FLOW CONTROL, CONVEYANCE, AND WQ FACILITIES
NO. 2 – INFILTRATION FACILITIES
Maintenance
Component
Defect or Problem Conditions When Maintenance Is Needed Results Expected When
Maintenance Is Performed
Inlet/Outlet Pipes Sediment
accumulation
Sediment filling 20% or more of the pipe. Inlet/outlet pipes clear of sediment.
Trash and debris Trash and debris accumulated in inlet/outlet
pipes (includes floatables and non-floatables).
No trash or debris in pipes.
Damaged Cracks wider than ½-inch at the joint of the
inlet/outlet pipes or any evidence of soil entering
at the joints of the inlet/outlet pipes.
No cracks more than ¼-inch wide at
the joint of the inlet/outlet pipe.
Access Manhole Cover/lid not in place Cover/lid is missing or only partially in place.
Any open manhole requires immediate
maintenance.
Manhole access covered.
Locking mechanism
not working
Mechanism cannot be opened by one
maintenance person with proper tools. Bolts
cannot be seated. Self-locking cover/lid does not
work.
Mechanism opens with proper tools.
Cover/lid difficult to
remove
One maintenance person cannot remove
cover/lid after applying 80 lbs of lift.
Cover/lid can be removed and
reinstalled by one maintenance
person.
Ladder rungs unsafe Missing rungs, misalignment, rust, or cracks. Ladder meets design standards.
Allows maintenance person safe
access.
Large access
doors/plate
Damaged or difficult
to open
Large access doors or plates cannot be
opened/removed using normal equipment.
Replace or repair access door so it
can opened as designed.
Gaps, doesn't cover
completely
Large access doors not flat and/or access
opening not completely covered.
Doors close flat; covers access
opening completely.
Lifting Rings missing,
rusted
Lifting rings not capable of lifting weight of door
or plate.
Lifting rings sufficient to lift or
remove door or plate.
Infiltration Pond,
Tank, Vault, Trench,
or Small Basin Filter
Bags
Plugged Filter bag more than 1/2 full. Replace filter bag or redesign
system.
Infiltration Pond,
Tank, Vault, Trench,
or Small Basin Pre-
settling Ponds and
Vaults
Sediment
accumulation
6" or more of sediment has accumulated. Pre-settling occurs as designed
Infiltration Pond,
Rock Filter
Plugged High water level on upstream side of filter
remains for extended period of time or little or no
water flows through filter during heavy rain
storms.
Rock filter replaced evaluate need
for filter and remove if not
necessary.
Infiltration Pond
Emergency
Overflow Spillway
Rock missing Only one layer of rock exists above native soil in
area five square feet or larger, or any exposure
of native soil at the top of out flow path of
spillway. Rip-rap on inside slopes need not be
replaced.
Spillway restored to design
standards.
Tree growth Tree growth impedes flow or threatens stability of
spillway.
Trees removed.
4/24/2016 2016 Surface Water Design Manual – Appendix A
A-4
APPENDIX A MAINTENANCE REQUIREMENTS FOR STORMWATER FACILITIES AND ON-SITE BMPS
12/12/2016 2017 City of Renton Surface Water Design Manual
A-12
NO. 6 – CONVEYANCE PIPES AND DITCHES
MAINTENANCE
COMPONENT
DEFECT OR
PROBLEM
CONDITIONS WHEN
MAINTENANCE IS NEEDED
RESULTS EXPECTED WHEN
MAINTENANCE IS PERFORMED
Pipes Sediment & debris
accumulation
Accumulated sediment or debris that
exceeds 20% of the diameter of the pipe.
Water flows freely through pipes.
Vegetation/root
growth in pipe
Vegetation/roots that reduce free
movement of water through pipes.
Water flows freely through pipes.
Contaminants and
pollution
Any evidence of contaminants or pollution
such as oil, gasoline, concrete slurries or
paint.
Materials removed and disposed of
according to applicable regulations. Source
control BMPs implemented if appropriate.
No contaminants present other than a
surface oil film.
Damage to protective
coating or corrosion
Protective coating is damaged; rust or
corrosion is weakening the structural
integrity of any part of pipe.
Pipe repaired or replaced.
Damaged pipes Any dent that decreases the cross section
area of pipe by more than 20% or is
determined to have weakened structural
integrity of the pipe.
Pipe repaired or replaced.
Ditches Trash and debris Trash and debris exceeds 1 cubic foot per
1,000 square feet of ditch and slopes.
Trash and debris cleared from ditches.
Sediment
accumulation
Accumulated sediment that exceeds 20%
of the design depth.
Ditch cleaned/flushed of all sediment and
debris so that it matches design.
Noxious weeds Any noxious or nuisance vegetation which
may constitute a hazard to City personnel
or the public.
Noxious and nuisance vegetation removed
according to applicable regulations. No
danger of noxious vegetation where City
personnel or the public might normally be.
Contaminants and
pollution
Any evidence of contaminants or pollution
such as oil, gasoline, concrete slurries or
paint.
Materials removed and disposed of
according to applicable regulations. Source
control BMPs implemented if appropriate.
No contaminants present other than a
surface oil film.
Excessive vegetation
growth
Vegetation that reduces free movement of
water through ditches.
Water flows freely through ditches.
Erosion damage to
slopes
Any erosion observed on a ditch slope. Slopes are not eroding.
Rock lining out of
place or missing (If
applicable)
One layer or less of rock exists above
native soil area 5 square feet or more, any
exposed native soil.
Replace rocks to design standards.
APPENDIX A MAINTENANCE REQUIREMENTS FOR FLOW CONTROL, CONVEYANCE, AND WQ FACILITIES
NO. 5 – CATCH BASINS AND MANHOLES
Maintenance
Component
Defect or Problem Condition When Maintenance is Needed Results Expected When
Maintenance is Performed
Structure Sediment Sediment exceeds 60% of the depth from the
bottom of the catch basin to the invert of the
lowest pipe into or out of the catch basin or is
within 6 inches of the invert of the lowest pipe
into or out of the catch basin.
Sump of catch basin contains no
sediment.
Trash and debris Trash or debris of more than ½ cubic foot which
is located immediately in front of the catch basin
opening or is blocking capacity of the catch basin
by more than 10%.
No Trash or debris blocking or
potentially blocking entrance to
catch basin.
Trash or debris in the catch basin that exceeds 1/3 the depth from the bottom of basin to invert
the lowest pipe into or out of the basin.
No trash or debris in the catch
basin.
Dead animals or vegetation that could generate
odors that could cause complaints or dangerous
gases (e.g., methane).
No dead animals or vegetation
present within catch basin.
Deposits of garbage exceeding 1 cubic foot in
volume.
No condition present which would
attract or support the breeding of
insects or rodents.
Damage to frame
and/or top slab
Corner of frame extends more than ¾ inch past
curb face into the street (If applicable).
Frame is even with curb.
Top slab has holes larger than 2 square inches
or cracks wider than ¼ inch.
Top slab is free of holes and cracks.
Frame not sitting flush on top slab, i.e.,
separation of more than ¾ inch of the frame from
the top slab.
Frame is sitting flush on top slab.
Cracks in walls or
bottom
Cracks wider than ½ inch and longer than 3 feet,
any evidence of soil particles entering catch
basin through cracks, or maintenance person
judges that catch basin is unsound.
Catch basin is sealed and is
structurally sound.
Cracks wider than ½ inch and longer than 1 foot
at the joint of any inlet/outlet pipe or any
evidence of soil particles entering catch basin
through cracks.
No cracks more than 1/4 inch wide at
the joint of inlet/outlet pipe.
Settlement/
misalignment
Catch basin has settled more than 1 inch or has
rotated more than 2 inches out of alignment.
Basin replaced or repaired to design
standards.
Damaged pipe joints Cracks wider than ½-inch at the joint of the
inlet/outlet pipes or any evidence of soil entering
the catch basin at the joint of the inlet/outlet
pipes.
No cracks more than ¼-inch wide at
the joint of inlet/outlet pipes.
Contaminants and
pollution
Any evidence of contaminants or pollution such
as oil, gasoline, concrete slurries or paint.
Materials removed and disposed of
according to applicable regulations.
Source control BMPs implemented if
appropriate. No contaminants
present other than a surface oil film.
Inlet/Outlet Pipe Sediment
accumulation
Sediment filling 20% or more of the pipe. Inlet/outlet pipes clear of sediment.
Trash and debris Trash and debris accumulated in inlet/outlet
pipes (includes floatables and non-floatables).
No trash or debris in pipes.
Damaged Cracks wider than ½-inch at the joint of the
inlet/outlet pipes or any evidence of soil entering
at the joints of the inlet/outlet pipes.
No cracks more than ¼-inch wide at
the joint of the inlet/outlet pipe.
2016 Surface Water Design Manual – Appendix A 4/24/2016
A-9
APPENDIX A MAINTENANCE REQUIREMENTS FLOW CONTROL, CONVEYANCE, AND WQ FACILITIES
NO. 5 – CATCH BASINS AND MANHOLES
Maintenance
Component
Defect or Problem Condition When Maintenance is Needed Results Expected When
Maintenance is Performed
Metal Grates
(Catch Basins)
Unsafe grate opening Grate with opening wider than 7/8 inch. Grate opening meets design
standards.
Trash and debris Trash and debris that is blocking more than 20%
of grate surface.
Grate free of trash and debris.
footnote to guidelines for disposal
Damaged or missing Grate missing or broken member(s) of the grate.
Any open structure requires urgent
maintenance.
Grate is in place and meets design
standards.
Manhole Cover/Lid Cover/lid not in place Cover/lid is missing or only partially in place.
Any open structure requires urgent
maintenance.
Cover/lid protects opening to
structure.
Locking mechanism
Not Working
Mechanism cannot be opened by one
maintenance person with proper tools. Bolts
cannot be seated. Self-locking cover/lid does not
work.
Mechanism opens with proper tools.
Cover/lid difficult to
Remove
One maintenance person cannot remove
cover/lid after applying 80 lbs. of lift.
Cover/lid can be removed and
reinstalled by one maintenance
person.
4/24/2016 2016 Surface Water Design Manual – Appendix A
A-10
APPENDIX A MAINTENANCE REQUIREMENTS FLOW CONTROL, CONVEYANCE, AND WQ FACILITIES
NO. 27 – GRAVEL FILLED DISPERSION TRENCH BMP
Maintenance
Component
Defect or Problem Conditions When Maintenance is Needed Results Expected When
Maintenance is Performed
Preventative Blocking, obstructions Debris or trash limiting flow to dispersion trench
or preventing spreader function.
Dispersion trench able to receive full
flow prior to and during wet season.
Site Trash and debris Trash or debris that could end up in the
dispersion trench is evident.
No trash or debris that could get into
the dispersion trench can be found.
Pipes Inlet is plugged The entrance to the pipe is restricted due to
sediment, trash, or debris.
The entrance to the pipe is not
restricted.
Vegetation/roots Vegetation/roots that reduce free movement of
water through pipes.
Water flows freely through pipes.
Plugged Sediment or other material prevents free flow of
water through the pipe.
Water flows freely through pipes.
Broken joint or joint
leaks.
Damage to the pipe or pipe joints allowing water
to seep out.
Pipe does not allow water to exit
other than at the outlet to the trench.
Cleanout caps Cleanout caps are broken, missing, or buried. Cleanout caps are accessible and
intact.
Structure Flow not reaching
trench
Flows are not getting into the trench as designed. Water enters and exits trench as
designed.
Perforated pipe
plugged
Flow not able to enter or properly exit from
perforated pipe.
Water freely enters and exits
perforated pipe.
Flow not spreading
evenly at outlet of
trench
Outlet flows channelizing or not spreading evenly
from trench.
Sheet flow occurs at the outlet of the
trench.
Cleanout/inspection
access does not allow
cleaning or inspection
of perforated pipe
The cleanout/inspection access is not available. Cleanout/inspection access is
available.
Filter Media Filter media plugged Filter media plugged. Flow through filter media is normal.
Inspection Frequency Annually and prior to and following significant
storms.
Inspect dispersion trench system for
any defects of deficiencies.
4/24/2016 2016 Surface Water Design Manual – Appendix A
A-36
APPENDIX E:
DOWNSTREAM ANALYSIS
APPENDIX F:
WWHM REPORT
WWHM2012
PROJECT REPORT
General Model Information
POC Thresholds
Landuse Basin Data
Predeveloped Land Use
Mitigated Land Use
Routing Elements
Predeveloped Routing
Mitigated Routing
Analysis Results
POC 1
Return Period Flow(cfs)
Return Period Flow(cfs)
Year Predeveloped Mitigated
Rank Predeveloped Mitigated
Flow(cfs) Predev Mit Percentage Pass/Fail
Model Default Modifications
PERLND Changes
IMPLND Changes
Appendix
Predeveloped Schematic
Mitigated Schematic
Predeveloped UCI File
Mitigated UCI File
Predeveloped HSPF Message File
Mitigated HSPF Message File
Disclaimer
Legal Notice